1. Field
The disclosure relates to envelope tracking for power amplifiers.
2. Background
Envelope tracking is a technique for increasing the efficiency of power amplifiers. In an envelope tracking (ET) system, the supply voltage of a power amplifier is dynamically adjusted to keep the power amplifier operating with sufficient headroom to maintain linearity, while nevertheless minimizing DC power consumption. The supply voltage of the power amplifier is commonly generated using a separate linear amplifier that tracks the envelope of the power amplifier output. In certain prior art implementations, the linear amplifier is itself coupled to an amplifier supply voltage generated by a boost converter, which is capable of generating a boosted supply voltage for the linear amplifier that exceeds the maximum supply voltage otherwise available to the system, e.g., a battery voltage. In this manner, the power amplifier output can reach and even exceed the battery voltage when necessary.
The amplifier supply voltage is typically set to be higher than the peak required power amplifier output plus some additional headroom voltage. In certain prior art implementations, this headroom voltage is a static value that is pre-programmed and not updated over time. However, as the preferred headroom voltage may vary considerably across different operating scenarios, e.g., across different processes, temperatures, load conditions, etc., a single static value for the headroom voltage may not be optimal in all cases. Furthermore, a headroom voltage that is chosen too low may undesirably lead to startup failure in the boost converter, which would compromise the linearity of the system.
It would be desirable to provide techniques for dynamically determining the optimal headroom voltage for an ET system according to the particular operating scenario, and further for preventing startup failure for boost converters in ET systems.